Partnership Capital and Distributions - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2013
Limited Partners Capital Account [Line Items]
General partnership interest and distribution right				2.00%
Common unit, Subordinated unit and General Partner Unit and Related Distribution Incentive Rights description				The Subordination Period will lapse at such time when the Partnership has earned and paid at least the minimum quarterly distribution on each common unit, subordinated unit and general partner unit for any three consecutive, non-overlapping four-quarter periods ending on or after June 30, 2013. Also, if the Partnership has earned and paid at least 150 percent of the minimum quarterly distribution on each outstanding common unit, subordinated unit and general partner unit and the related distribution on the incentive distribution rights in a consecutive four-quarter period, the Subordination Period will terminate.
Maximum
Limited Partners Capital Account [Line Items]
Maximum percentage of cash that can be distributed for general partner				50.00%
Cash Distributions for Limited and General Partner
Limited Partners Capital Account [Line Items]
Cash distribution period				45 days
Cash distribution paid	$ 93.3			$ 177.4
Cash distribution per unit		$ 0.4675	$ 0.45
Cash distribution declaration date	Jul. 24, 2013
Minimum Quarterly Distribution
Limited Partners Capital Account [Line Items]
Common units received distribution per unit				$ 0.3375